New Colors() class

[glenn-jocher]

@kalenmike @SergioSanchezUltralytics

This PR implements improvements to the YOLOv5 colors by creating a new Colors() class that handles datatype and modulus operations automatically and provides BGR order support. All colors are now centralized and sourced at one location, and detect.py is now brought under the same color palette as the rest of the github repo.

This will also allow for single-point substitution of our own Ultralytics color palette when it's ready.

🛠️ PR Summary

_{Made with ❤️ by Ultralytics Actions}

🌟 Summary

Improved color handling for bounding box visualization in YOLOv5.

📊 Key Changes

• Refactored color generation into the Colors class within utils/plots.py.
• Removed redundant color list generation from multiple files (detect.py, models/common.py, and utils/plots.py).
• Adjusted color usage to call the colors class instance when plotting bounding boxes.

🎯 Purpose & Impact

• This change centralizes the color management for visual elements, which leads to more consistent use of colors across the project.
• The impact on users includes more uniform visual outputs and potentially fixing any inconsistent color applications previously present.
• Developers benefit from a cleaner, DRY (Don't Repeat Yourself) codebase with a single source of truth for color choices.
• The refactoring may make it easier to maintain and adjust visual styling in the future, as there's now a single place to make changes to the color palette.